Radio frequency (RF) electronics systems are commonly used for communications, radar threat warning, direction finding, and other applications. Many RF electronics systems specify limits on the weight, dimensions, and physical profile of their associated antenna systems. For example, mobile platforms (e.g., airborne, vehicle-borne, and human-borne platforms) may particularly specify strict limits on the physical characteristics of an antenna and other system components associated with the antenna, such as support structures and processing electronics. The physical characteristics of an antenna may vary greatly, depending on the particular antenna technology used, the bandwidth that the antenna is designed to support, and other factors. In airborne platforms, for example, commonly used antenna technologies include phased array antenna systems, surface acoustic wave (SAW) based antenna systems, and monopole or slot antenna systems.
An antenna system typically includes the antenna element, itself, along with associated mounting and support structures and processing electronics. An antenna system may also consist of an array of antenna elements arranged in a planar configuration for increased gain and directivity. RF energy may be received via “slots” associated with the antenna array. When used in conjunction with an airborne platform, the slots may be formed through a surface of the aircraft “skin” or outer covering. To achieve reasonable performance, the in-plane dimensions of each receiving antenna element typically are selected to have a size of at least one-half wavelength of the lowest frequency limit of the intended bandwidth. Accordingly, given a fixed number of antenna elements, the overall dimensions of an array antenna increases as the lower bandwidth limit increases. These characteristics of array antennas makes them unsuitable or non-optimal for some platforms having restrictive antenna weight and size specifications, as well as for platforms in which interruptions (e.g., slots) in the outer surface may be undesirable. These restrictions become more severe at lower frequencies, such as frequencies in a range of about 1 to 100 Megahertz (MHz).
Other types of systems may include a ground plane, which is adapted to carry currents produced from RF energy incident upon the ground plane. In some of these systems, antennas may couple to the system's ground plane (e.g., a portion of an aircraft's outer covering), and may draw power from induced currents flowing in the ground plane. These types of systems may include, for example, surface acoustic wave (SAW) devices and/or monopole (or slot) antennas, which are positioned above and in contact with the ground plane (or formed by an opening in the ground plane, with a backing cavity). Although these types of antennas are suitable for use on some platforms, they also may be unsuitable or non-optimal for others. For example, in some cases, the antenna profile above the ground plane may cause undesirable effects (e.g., decreased aerodynamic efficiency).
For the above reasons, it is desirable to provide antenna elements, antennas, and systems that may support a wider range of bandwidths while having physical dimensions and profiles that are within the specifications of restrictive platforms. In addition, it is desirable to provide antenna elements, antennas, and systems that do not include significant physical interruptions in the ground plane (e.g., slots) or require appreciable modification to the structure (e.g., backing cavities or protruding monopole elements). Other desirable features and characteristics of embodiments of the inventive subject matter will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and the foregoing technical field and background.